


Biological Cycles of the Lunarly Inclined

by tsukinofaerii



Category: Teen Wolf (TV)
Genre: Crack, M/M, Menstruation, Werewolf Biology
Language: English
Status: Completed
Published: 2013-05-15
Updated: 2013-05-15
Packaged: 2017-12-12 00:17:04
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,902
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/804906
Author URL: https://archiveofourown.org/users/tsukinofaerii/pseuds/tsukinofaerii
Summary: <blockquote class="userstuff">
              <p>Erica has a problem and Stiles is going to find a solution. (Or else.)</p>
            </blockquote>





	Biological Cycles of the Lunarly Inclined

**Author's Note:**

> This was mostly created as an experiment in train of thought and fucking around when I should have been writing other things but didn't wanna. Also as an excuse to play with the idea of werewolf biology, because it's kind of fascinating to ponder. The Derek/Stiles is very minor.

"Stiles! There's a girl here to see you!"

Stiles froze where he was sitting at his computer, wasting away a fine summer day on a dozen different websites (only one of which was porn, thank you; he tried to maintain a plausible deniability level of browsing). Downstairs, he heard his father letting someone in, the sound of high heels echoing on the hardwood floor in the living room. 

It couldn't possibly be Lydia. Why would it be? He'd only spent most of his life trying to lure her into his home, where he could woo her as was appropriate for a goddess of long division (math books, chocolates and a bottle of wine his father didn't know he'd purloined). Ever since the kanima issue had been resolved, she hadn't had two words to say to him, and with school out for the summer he didn't have an excuse to stare at the back of her lovely head on a daily basis (Econ and English). So why would she—

"Stiles!"

"Coming!" Hurriedly, he grabbed up his discarded pants (it was hot, okay?) and started shimmying into them, one hand on the waistband while the other snatched up scattered dirty socks, "used" socks and old underwear, tossing them into the hamper with accuracy he'd never managed on the lacrosse field. He was barefoot, but he was also in his own home, and Scott had once said he had nice feet. Of course, Scott worked with neurotic poodles whose owners painted their nails, so maybe that wasn't much of a compliment. 

" _Stiles_!"

"I'm _coming_!" Taking one last glance around his room (why had he bothered when she was downstairs?), Stiles yanked open the door and bolted for the living room, still buckling his belt. 

The stairs he took two at a time, resulting in a near nosedive when the bottom step didn't line up with his pattern. He caught himself with something like grace (if Grace was a drunken penguin) and finished with an also-graceful stagger into the living room, grabbing his father's shoulder to keep from ( _gracefully_ ) sliding right into the wall. "I'm here, I'm here! Hey Lyyyyyyerica?"

Erica Reyes sat on his father's couch, legs crossed at the knee, all black leather and heels that could be used as stabbing instruments in a particularly messy murder. And when he said all black leather, he meant _all black leather_. Her boots were black leather, her miniskirt was black leather and—of course—she had one of the Werewolf Monthly Club jackets on. (He ignored that she was wearing a leather jacket in summer. Stiles had stopped questioning werewolf sartorial choices when Scott stopped recognizing the difference between argyle and plaid and tried to wear both at the same time. There were some things that even the fashion-deprived couldn't tolerate.) It wasn't even her jacket, but one of Derek's—he could tell by the way it hung off of her shoulders. And also by the faint scent of cologne, overabundant masculinity and angst that hung in the air like a patina of bad life choices.

Not that he'd memorized Derek's scent that one time they'd been paralyzed on the floor of his father's office together. Nope nope nope. It was just a guess, that was all. (He totally had, and it had been the only good thing to happen that night.)

"I'll leave you two to talk," his father said, slipping out from under Stiles' hand. "Have fun, and let me know if you leave."

"Will do, Dad, thanks." Stiles hand a hand over his hair, feeling the not-really-there prickle where it had started to grow out because he'd been too lazy to keep up with it. "What are you doing here?" Her eyes narrowed, and he hastened to cover his ass before it was handed to him. "Not that I'm not delighted to see you, but..." 

"Stiles." Erica uncrossed her legs, expression hard and accusatory. She kept her knees pinned tight together, and her fingers had just a hint of claw where they rested on her thighs. "I haven't had my period in two months. Want to tell me why that is?" 

His father, who had been on the way to the kitchen to most likely indulge in some delicious, fatty goodness of the type he knew Stiles would frown about, did an abrupt about-face and marched right back into the living room. He planted himself between the couch and the door, arms crossed. "Yeah, Stiles, want to tell us why that is?"

Never in his life had Stiles ever felt more put on the spot. Erica looked close to following through on the many and varied threats Derek had heaped on him, and his father—while less visibly violent—didn't look much happier. He glanced back and forth between them, mouth working as he tried out various answers and they all came up short. "I don't—you—why—" Finally, he gave up, throwing his arms up to the uncaring sky (ceiling) and collapsing into the nearest chair. "You hate me, don't you?" he asked Erica bitterly. "Wouldn't you rather punch me again instead? Car part of your choice."

He'd been afraid she'd keep it up, but apparently pity hadn't completely left Erica behind. Her glare cracked into a smile. Which, of course, she turned on Stiles' dad rather than him. Hot girls only smiled at him before they beat him up. "Don't worry, Mr. Stilinski, I didn't sleep with Stiles. I like my men more... experienced."

The part of Stiles' brain that was capable of filtering a dozen different topics at once filtered that one right into the trash. _Nope, not thinking about it._ "But could this be—you know—" Stiles was rapidly losing his ability to pretend coherence. On top of that, he was starting to doubt his readiness to have his V-card punched. One of the better pieces of advice he'd ever heard was that if you couldn't talk about it, you shouldn't do it. (Scott's mom, during The Speech They Never Ever Spoke of Again.) On the other hand, he didn't think he'd ever be ready to talk about setting living people on fire and he'd already done that, so maybe there was a gray area. "Someone else?"

The glare was back. Weirdly, that was comforting. If Erica wanted him dead, something was right in the world. "If there was a chance I'm pregnant, do you think I'd come to _you_?" 

But then a thought hit him right in the mouth, and of course he had to vomit it out. "What about Derek? I thought you two were..." He made a gesture that he hoped wasn't too obscene. " _Together_." 

She made a face, all tight lipped and adorable scrunched nose. "Does he look like someone who's getting laid on a regular basis?"

"...Okay, you have a point there," Stiles had to concede. There were fewer people wound quite as tight as Derek. Even when paralyzed and floating in a pool, he'd been tense. (Slightly more pleasant than the time on the floor, even with the imminent peril of drowning, since his dad hadn't been in danger. Stiles still had occasional trouble with the scent of chlorine, though, which caused some issues when it came time to scrub the toilet.) 

"Besides," Erica continued, "I kissed him once and he threw me across the room. I think he likes dick more than boobs."

That was... not information Stiles needed to be thinking about in front of his father and a girl who could (and would if needed) drop a car on him at even the hint of a popped boner. "Oh." 

"So, _Erica_." Stiles' dad, king of smooth, sat down on the arm of the chair. Being Stiles' dad, he missed, recovered, and succeeded on the second try. (Stilinski men, fuck yeah.) "If you and my son aren't together, why _did_ you come here?"

It was like a switch was flipped. Erica's smile grew teeth and she leaned forward, deliberately displaying cleavage that Stiles knew, _knew_ looking at would get him in trouble. "Oh, you know," she said, voice surprisingly sweet for someone who was visibly contemplating the cannibalism option. "Stiles is good at finding out things. And the eye candy isn't bad." 

She wasn't looking at Stiles.

 _God_ , his life was unfair. 

His father (bless his Sheriff-y soul) was as obviously uncomfortable as Stiles could have asked him to be. "Why don't you speak to your mom? Or a doctor?"

"A doctor?" Another shift of Erica's weight slipped her skirt higher up her thighs. "We could _play_ doctor—"

"Whoa whoa whoa, hold it right there!" Stiles yelled, flailing himself upright (and almost smacking his father in the face, but some things you forgave family). "No hitting on my dad. None. _Nada_."

Erica rolled her eyes, but her posture changed enough that it wasn't like staring into a boob abyss. "Will you help or not?" 

"If you promise to leave while my dignity is still intact," Stiles offered, and the _look_ she gave him just wasn't right. "Or just leave." 

"Deal." Erica didn't have dimples, but her smile needed them. She stood up, pulling down her skirt as she did so. (Using an exorbitant amount of wiggle, if Stiles was any judge, and he rather thought of himself as a connoisseur of girl-wiggle.) "I'll talk to you later. Nice meeting you, Sheriff." 

Neither of them moved as she sashayed ( _sashayed_ , seriously, his life was a porn without the sex and had he mentioned that was unfair?) out the door, using the pointed toe of her high heel to pull it closed rather than the doorknob like any other reasonable human being (or werewolf).

For several long, blissful seconds things were quiet. Then his father said, "Are you _sure_...?"

Stiles sank back into the chair. He was one with the chair, forever and aye, marching ass in cushion together through the dark valleys of life. "Very sure. If she tapped this, believe me, I'd still be limping."

It would have done Stiles' self-esteem a service if his father had objected, or even made a comment about how he'd get there one day and _don't give up_. Anything about condoms would have helped. Instead, his dad just made a face ( _that_ face, the _I can find nothing to object to in that though I probably should_ face) and nodded, sliding off the chair arm. "Just checking. Pizza good for dinner?"

 _The cheesy, thin-crust dinner that was built out of the crisped remains of his soul._ "At least one vegetable," Stiles grumbled, without his usual effort.

"Congress says tomato sauce is a vegetable," his dad called, vanishing into a kitchen.

"And when is Congress ever right?" Stiles yelled back. "One vegetable!"

"My money, my toppings!"

At least _some_ things in his life were normal.

* * *

Stiles was a curious guy. Many had been the times he'd gone on a Wiki Walk and had come up three days later only when his computer crashed under the weight of all the open tabs. He read the dictionary for _fun_. The Mythbusters were his bros (he'd only semi-seriously considered sending in a request for a werewolf episode, mostly because Scott would never forgive him). 

Which was exactly why the first thing he did after Erica left (besides wallow in his own ignominy and eat the meat off his dad's slices of pizza) was to close his laptop and hide the battery and cord deep in his closet. No laptop meant no easy research meant no horrifying and unwanted information about the female reproductive system. There was always the library, if he really started to feel the itch to learn, but it was a lot harder to stumble over felching porn by accident there. Generally, library books were safe havens for the unwary, unlike Google. 

Three days later, a gutted squirrel was left on his windowsill, next to his previously hidden cord and battery.

_Point taken._

He got to work.

Menstrual cycles, as it turned out, were basically as emotional and erratic as Scott after a three day Disney marathon. Stress could throw it off. Diet could throw it off. Even just being around other women could throw it off. As far as Stiles was able to tell, there was indeed a God because a miracle was just about the only way women could reliably get pregnant. Two months was unusual and something to keep an eye on, but not really _weird_. At least with Erica, he could count out the worst possibilities

"It probably isn't cancer." 

Stiles could practically hear her eyes roll on the other end of the line. He'd called after spending two hours on Google realizing that he was on a wild goose chase. "I know _that_ ," she said sharply. "What else do you have?"

"It could be anything _other_ than cancer." She couldn't see him (probably—werewolf creep was a very real problem in his life) but he shrugged anyway and kicked his feet up onto his desk. "Did some other women join the pack? Have you changed medications or anything lately?"

She growled. She actually fucking growled, and it was just as terrifying as if she'd been there in the room with him. Maybe even more terrifying. If she had to run him down, that just gave her time to think of new and exciting ways to eviscerate him. "I'm a _werewolf_ , I don't take medication anymore. Try harder!"

Erica hung up. 

His _life_ , ladies and gentlemen.

But something she'd said niggled at the back of his brain, where all bad thoughts went to pester him until he gave in. _I'm a werewolf_. He'd been researching humans, on the basis that it was what would be relevant. But if she hadn't had a period in two months, and she'd only been a werewolf for _three_ , then there might be something worth looking into.

It could have been a coincidence, or the stress of the change, or just a regular diet of Thumper and Bambi combined with lower body fat making her usual cycle erratic. It didn't matter, though. If he didn't want to end up like that squirrel (he'd given it a backyard funeral; the neighbors didn't even notice when he did weird things back there anymore), no stone could be left unturned.

Groaning, Stiles let his head sag backwards so he could stare up at the slight discoloration on his ceiling that looked a little like England. "To the library, Watson!"

No one answered. He really needed to look into getting a sidekick one day.

* * *

The Beacon Hills Public Library was surprisingly well-stocked with books about supernatural beasties. Like, ridiculously so. They had their own set of shelves, and most of them were the kind of old, leather-bound monstrosity that was usually called a _tome_ and could be found in the back of a creepy occult shop that sold haunted merchandise and then vanished so you couldn't get a refund after it ruined your life and ate your dog. 

Since Scott had been bitten and the whole furry conga line had started up, Stiles had taken to assuming that it was because Beacon Hills had been the home of a werewolf pack since its founding. After all, books, like other predator species, often migrated to fill an ecological (or knowledgelogical) niche. (The hypothesis was a work in progress.) They weren't allowed to be checked out, but Stiles had never faltered in the face of a little larceny for the better good. 

Which would have been fine, if there'd been anything worth stealing.

There were maps of territories and hunting locations, spell books, giant monsters of books that could have put _Hogwarts: a History_ to shame and definitely wouldn't have fit in his backpack. In the space of an hour, Stiles learned that it was the magnetic effects of iron rather than any symbolic purity that turned off faeries, that blood-sucking vampires weren't real (but dick-sucking ones were, and would also swallow your soul along with your ejaculate so it wasn't as cool as it sounded) and that the one lake everyone avoided because people died there a lot was probably home to a thing called a kappa. Or a siren. Or possibly just an asshole water sprite with a penchant for murder.

And, of course, there was porn. Because Google wasn't traumatizing enough on its own.

What there _weren't_ were any biology books, except for one on Bigfoot printed in 1982 that claimed the beast was actually the ghost of Abraham Lincoln on the eternal hunt for his murderer. (It was nonfiction. Stiles' soul _wept_.) Even his old friend _On ye Warewolfe_ —usually a reliable source with minimal bullshit—failed to push beyond basic speculation about the link between the wolf and the lunar cycle. The closest it came to women was a detour into discussing lunar madness as a link between lycanthropy and women and how both should be kept locked up for their own protection. From there _On ye Warewolfe_ descended even farther into _On ye Misogyny_ for another three pages and Stiles just gave up before he read something that would get his balls deservedly clawed off.

 _Books_! Bastions of knowledge and also danger. Who knew?

As he trudged out, leaving the library unfortunately free of theft for the day, Stiles had to accept one unfortunate fact: in all Beacon Hills, there was only a single reliable resource for knowledge of werewolf bits and dongles and how they worked or failed to work. And that was Derek Hale. 

_Fuck._

* * *

Derek lived in a loft. 

Well, he called it a loft. Stiles called it a slightly less depressing pit of despair. It had a giant hole in the wall to complement the stained glass windows and utter lack of furniture. Which, considering Derek's continuing poor judgment in living spaces, was probably some sort of major werewolf status symbol. Muscles of titanium, teeth fit for the fairytale of your choice, and some sort of structural defect declaring you have no need for such puny things as protection from the elements. 

Or, in fact, from squirrels.

"Really, Derek?" Stiles stared at the squirrel in the rafters. It looked like it had made a nest up there somewhere. He was pretty sure squirrels were a bad thing to have in a building. On the other hand, Giant Hole in the Wall. By comparison, a minor rodential infestation seemed the lesser of worries. 

"Shut up, Stiles." Derek was doing a masterful job of ignoring the elephant in the room by resting one foot on the stairs (iron spiral, as if the place weren't already a pile of clichés) and reading a one of the Star Wars novels. The other foot was planted firmly on the ground, spreading his legs obscenely wide. Did Stiles mention that he was flat on his back and shirtless? Because he was flat on his back and shirtless.

God damn it. 

Trying to subtly adjust his half-boner as he walked, stiles prowled around the open space Derek laughingly called a living room. Or he would have, if Derek ever laughed at anything that wasn't someone's pain. The closest thing to a seat was a couple of old milk crates in the corner. He dragged one out, angling it so he could have the best view of Derek's exposed chest and abs without being obvious in his ogling. 

From the look Derek was giving him, not being obvious was very obvious. Or maybe werewolves could smell boners. 

Probably both, knowing his luck. The knowledge of which turned his boner into a fear boner, and it really said a lot about his life that his initial bodily reaction to terror these days was to get hard as a rock. Adrenalin was no fucking excuse. 

Stiles settled in on his crate, stretching his legs out so they weren't bunched up at his chest. "So."

"So." Derek didn't put the book down, but his eyes were angled more in Stiles direction than in its. That was a sort of victory. Any attention was good attention.

(God, he really hoped werewolves couldn't smell arousal. Maybe he'd tried to get Scott to use that once for his benefit, but it really wasn't worth it. Especially with how badly that turned out at the time.) 

"I need to know about werewolf gynecology." 

Derek, damn him, didn't even flinch. His book went down, his eyebrows went up, and he said, "You're not fucking Erica. She'd gut you, and I'm not giving you the bite to save your life."

" _Rude_. True, but rude." The way the book shadowed Derek's abs was nearly pornographic. No, scratch the nearly. It _was_ , because Derek was shirtless, and the way he'd laid the book on his body basically pointed straight at his happy trail, which in turn pointed at his ridiculously tight jeans that showed off exactly how much of an alpha male he was without him even needing to get hard. _Unfair_. "I'm asking _for_ Erica. She tromped into my house a week ago, made my father think I'm going to be a baby daddy and threatened my life if I don't figure out what's going on down there for her. Books and the internet have failed me. You're all I've got, dude."

It took a second for words to penetrate (ohhh bad word, Stiles, _bad word_ ) Derek's skull. Possibly the hair gel formed a barrier of some sort. His eyebrows drew together, and his mouth turned down in a frown that was more frowny than usual. Then, he sat up. Not propped himself up with his arms like a normal person, no. He just flexed those ridiculous abs and went from horizontal to vertical with minimal visible effort and maximum visible sexiness.

In his pants, Stiles' dick did something similar.

Finally, after the data had finished cycling through Derek's Human to Werewolf translator, he asked, "What's wrong with Erica?"

Stiles threw up his arms and sagged down, incidentally bringing up his knees. (Concealment action one is a go!) "That's what I'm trying to find out!"

Heaving a sigh (muscles, God damn _muscles_ ), Derek pinched the bridge of his nose. "Tell me."

So Stiles did. He took a detour around Erica flirting with his father, since he was busily trying to suppress that particular memory, and tried to focus on everything else. Like the implied pregnancy, and how his dad was _still_ watching him like he might spontaneously erupt into teenage fatherhood at any second. (Which, please, Stiles knows the value of condoms and birth control, even if he hadn't exactly had a chance to use them himself much. Or ever.) About the time Derek started to look (more) murderous, he got on with the complete lack of help that was the known world of knowledge. 

"... and so here I am, ready to throw himself on your extremely questionable mercy," he finished with a grand gesture that, he hoped, took in the loft and its abundant airflow. 

Derek's face was made of stone. "And?"

"...Aaaand?" Stiles stared at Derek. "And now here's where you tell the answer." 

Murder. There was murder happening in Derek's head. He glared at Stiles. "You haven't even told me what's _wrong_."

 _Oh_. "Oh." He scratched his head sheepishly. "She said she's missed two months of her period, and she's sure she's not pregnant, and that it's not yours if she is. Which she's not."

Derek blinked. Then he sighed and flopped back down to the bare floorboards with a rising cloud of dust and a smack of flesh. He picked up his book, flipping back to where he'd left off. "Go home, Stiles." 

Okay, that hadn't been the answer he'd expected. "What?"

"I said, _go home_. She's pulling your leg." Pointedly, Derek licked a finger and flipped the page. He actually _licked his finger_ , who _did_ that? "I already talked with Erica about this after I bit her. She knows it's normal." 

_It is?_ "It is?" (He had to stop being an echo chamber for his own thoughts, it was getting annoying.) 

"Yep." Another finger-lick, and now Stiles suspected Derek was fucking with him. He was playing boner mind games on helpless teenagers. That was just _cruel_. "Werewolf females don't go through a monthly cycle. They hit a fertile peak twice a year, and only bleed if they don't get pregnant. Erica probably just wanted to embarrass you." 

Well, that didn't seem right. "There's much easier ways to embarrass me," Stiles pointed out. "You're doing it right now."

True to asshole form, Derek just smirked. Which meant yes, he knew what effect he was having on Stiles' poor abused teenage hormones and he was doing it anyway. _Bastard._ "It's been a slow summer. Maybe she was bored." 

That was... sadly true. It _had_ been a slow summer. Or maybe the winter had just been that bad. "Okay, so let's say that all of this has been for nothing." Since he didn't have anything to hide anymore, Stiles slipped off his crate, letting his butt smack onto the floor. It actually left his tailbone buzzing weirdly from the impact, like it was a funny bone, but less funny. "Erica knew, ha ha, we all had a good laugh. That doesn't mean you're getting out of this. If I've had to spend a week—" three days researching and three days avoiding, but it was still a week "—looking all of this up, you can at least explain it to me. Using words."

Derek's eyebrows did something complicated that seemed to simultaneously imply that Stiles was an idiot and that he was planning something nefarious. They must have had training from a Bond villain. "I'm not giving you the sex talk, Stiles. Why don't you ask Scott if you're that interested?" 

There was a punchline somewhere in there. Or maybe Stiles was the punchline. "Why would I ask Scott when I can ask you?" he asked, very reasonably he thought. "You're right here." 

"He might answer you." Long fingers fiddled with the edge of the book, stroking the cover, and really, Stiles was _this close_ to calling foul. "You don't want me to."

If he didn't know better, Stiles might have thought Derek was flirting with him. (Actually, he _didn't_ know better, but thinking too hard about that might turn his problem boner into a problem wet spot, and that just wasn't cool.) "How do you know that?" 

There wasn't anything to really pin-point it, but suddenly Stiles knew he had Derek's full attention. It wasn't all that different from standing in the middle of the road while a semi-truck bore down on you. There was a little exhilaration and a lot of terror and, yes, the ever-present fear-boner that was Stiles' life.

Derek closed his book. 

"How about," he said slowly, "we have a little demonstration?"

* * *

The next day found Stiles collapsed in a pile of pillows four layers deep when Scott walked in for their scheduled Whedon Marathon. He stood in the doorway, blinking in confusion as Stiles carefully laid out their options in order of maximum number of asses kicked. 

"Dude?" Scott asked, shifting from foot to foot like he was close to running. "What are you... Are you okay?"

"No," Stiles said sharply, slapping the Avengers down on the bedspread next to Buffy Season 1. "No, Scott. I'm not okay. Close the door and sit down." 

"Um?" But Scott did as he was told, apparently using some sort of wolfy sixth sense to tell that Stiles meant business. He closed the door and sat on the very, very far edge of the bed, presumably where he thought he'd be safe. "Okay. Why do you smell like you're hurt?"

"Because I am." Organization laid out, Stiles stared down at the smiling faces of a lot of dead people. "I'm very hurt, because someone's been keeping secrets."

"Secrets?" 

Stiles didn't have to look up to know that Scott's eyes were wide, and getting wider. They were bros that way. Or they were. _Were_ , because bros didn't keep monumental information from each other. 

"Secrets," he repeated. "Now, we're going to watch all of these, and we will laugh and cry and throw things. But first..." Stiles took a deep breath, made as stern a face as he could, and looked up into Scott's horrified eyes. "First, you're going to tell me _everything you know about tying_."

They stared at each other. 

Scott bolted for the door. 

"Get back here you coward," Stiles shouted, lunging after him only to be pulled up short a sharp twinge from his abused ass muscles. He ended up flopped face-first on the bed as Scott pounded down the steps. A moment later the door slammed shut as he made a break for freedom. 

" _Traitor_!" Stiles yelled, knowing that his werewolf ex-bestie (okay, who was he kidding, always-bestie, kinky sex secrets or no) could hear him just fine. "Come back and tell me about your dick!"

A shoe scuffed on the carpet outside his door. Stiles slowly looked up into his father's slightly horrified and a lot resigned face. 

"Do I want to know?" he asked.

There was nothing for it but to collapse face-first to the bed. "No," he mumbled, hoping deep in his heart that he'd suffocate in his ass pillows, "you really don't."

"... Okay then."

The door closed, leaving Stiles alone with his shame and ass pillows. It was for the best, really.


End file.
